In order to power an electromechanical actuator having a polyphase motor including windings that form phases, it is known to use power supplies comprising two inverters connected in series. Each inverter has a voltage source with its terminals connected to as many arms as there are windings for powering on the machine. Each arm comprises an upstream controlled switch and a downstream controlled switch connected in series. Each winding has a first end connected to one of the arms of one of the inverters, at a point that is situated between the controlled switches of said arm, and a second end connected to one of the arms of the other inverter, likewise at a point situated between the controlled switches of said arm.
If one of the controlled switches in one of the arms of one of the inverters fails, so as to remain permanently open or closed, it is known to close certain switches of the inverter in question and to open its other switches so as to create a common point between the ends of the windings connected to said inverter, which common point is connected to one of the terminals of the voltage source. Since the two voltage sources are connected to grounds that are distinct, the common point is neutral from the point of view of the other inverter, and it therefore becomes possible to control the machine solely from the other inverter, thereby continuing to ensure operation of the rotary machine with torque that is substantially constant.
Such an architecture is thus capable of withstanding the failure of one of the controlled switches. Nevertheless, such an architecture does not make it possible to continue operating the rotary machine correctly if the end of one of the windings becomes disconnected from the corresponding arm. For example, on a three-phase rotary machine having one of its windings disconnected, there still remain two phases that can be controlled. If the switches of the inverters continue to be controlled as though one of the windings had not become disconnected, then the machine would be subjected to torque with a high degree of ripple, which can be very harmful in certain applications, for example actuating high-lift devices of an aircraft, or actuating landing gear.
As described above, it is possible to seek to create a common point between the two good phases by opening and closing the switches one of the inverters appropriately. Nevertheless, the two phases as interconnected in this way via a common point can be controlled only by using currents that present a sum that is zero, which currents therefore need to be phase offset at an angle π, which, in combination with the phases being spatially offset by 2π/3, likewise leads to torque with a high level of ripple.